The invention relates to a plasma display panel comprising:                a rear tile provided with an array of address electrodes;        a front tile, parallel to the first one, provided with an array of pairs of sustain electrodes leaving between them a sustain discharge gap, one of the electrodes of each pair being arranged with respect to an address electrode so as to leave between them, and between the tiles, address discharge spaces.        
Such a panel is called a coplanar panel because the main direction of the sustain discharges is parallel to the tiles.
The intersections between the address electrodes and the pairs of sustain electrodes form discharge spaces between the tiles; these discharge spaces are in general bounded by barriers which themselves form an array and serve as spacers between the tiles.
The spaces bounded by these barriers form cells, the walls of which are in general coated with phosphors; these cells and the space between the tiles are filled with a low-pressure gas suitable for obtaining discharges which emit ultraviolet radiation.
When the display panel is in operation, electrical discharges are generated in the gas of the cells, which discharges emit ultraviolet radiation towards the phosphors on the walls of these cells; the phosphors, excited by this ultraviolet radiation, emit visible radiation through the front tile towards the person observing the image displayed by the panel.
In the case of panels emitting three primary colours, namely red, green and blue, the adjacent cells have phosphors of different colours so that discharges emitting indirectly in the red, green and blue are obtained.
To prevent the electrodes of the front tile absorbing too great a part of this visible radiation, these electrodes are preferably made in a material which is both conducting and transparent, such as tin oxide or a mixed indium-tin oxide (ITO); since these transparent electrodes are in general not sufficiently conducting, the arrays of transparent electrodes are “duplicated” with opaque metal conductors called buses, because they distribute the electric current for the discharge to the transparent electrodes.
A description of such arrays of sustain electrode pairs for a front tile will be found in documents JP 11-297214 by Pioneer (FIG. 1), JP2000-123748 by NEC (FIGS. 5 to 7) and EP 0 993 017 by Fujitsu (FIG. 11), these being repeated in FIGS. 1, 2 and 3 below; the discharge gaps 5 are bounded by the straight edges of the discharge ignition conductors 2, each connected via connection shunts 4 to a metal bus 3; in FIGS. 1 and 2, the ignition conductors 2 are continuous and transparent, the shunts 4 also being transparent; in all the figures, the metal conductors 3 are continuous, opaque and placed along the edges of the cells, or even beneath the barrier separating two cells, so as to absorb as little as possible of the radiation emitted by the phosphors.
In document EP 0 802 556 by Matsushita (FIGS. 7, 9), the connection shunts are placed between the discharge regions, above the barriers separating these regions, where they cannot participate in spreading the discharges.
Thus, it may be considered that each electrode 1, 1′ of the sustain array described in these documents is in the form of a ladder, one of the rails of which corresponds to the transparent ignition conductor 2, the other rail of which corresponds to the metal conductor 3 and the rungs of which correspond to the shunts 4; such a configuration of sustain electrodes allows the luminous efficiency of the discharges to be improved.
This is because, when a sufficient electrical voltage (the sustain voltage) is applied between two electrodes 1, 1′ of the same pair, a discharge is ignited in the gap 5 at the outer edge of the ignition conductor 2, over a front which can extend over the entire width of the cell in the lit state. After ignition, the discharge extends towards the bus 3 along the shunt 4 of this cell, the discharge thus spreading out in a general direction approximately perpendicular to the ignition front. The discharge front then narrows to the width of this shunt 4 and, because of this narrowing, the discharge advances towards the bus very rapidly. On reaching the bus 4, the discharge front widens again, the discharge reaching its maximum advance and its maximum extension, as shown schematically in the central cell of FIG. 3. As long as the transferred charges are insufficient to create a reverse potential, the discharge is sustained at this extended stage.
The use of wide electrodes is necessary in a coplanar structure in order to obtain a high efficiency in converting the electrical energy into light energy, since the luminous efficiency of the discharge is strongly related to its spread lengthwise and the luminance to its width. The longer the electrodes, in order to allow extensive spreading, the better the luminous efficiency will be.
The rapid spread of the discharge and the longest possible time for which it is sustained in the state of maximum extension are essential elements for improving the luminous efficiency of the discharge. The shunts 4 therefore serve as both means for electrically connecting the ignition conductors 2 to the metal buses 3 and as means for guiding and accelerating the propagation of the discharge. As discharge-spreading means, the shunts 4, whose width is very much less than that of the ignition front, are tailored in order to narrow the discharge front with respect to the ignition front; this narrowing is one means of reducing the electrical capacitance and makes it possible to accelerate the propagation of the discharge; other capacitance-lowering means, such as the localized increase in the thickness of the dielectric layer when it is present above the shunt, allow the propagation speed of the discharge to be increased.
Document EP 0 782 167 by Pioneer (FIG. 15) also describes an array of ladder-shaped sustain electrodes according to one particular embodiment. The width of the rungs 4 can vary, being narrow in the part which adjoins the ignition conductor 2 but much wider in the part which adjoins the bus 3 of the electrode.